Late Jurassic-Early Cretaceous Erg Deposits in the Mengyin Basin, Western Shandong Province, China: Inferences about the Wind Regime and Paleogeography

The Late Jurassic-Early Cretaceous Santai Formation, sporadically distributed in western Shandong Province, comprises terrestrial alluvial-eolian successions, which records regional wind patterns and paleogeography in eastern North China. This paper conducts an analysis of eolian stratification, bounding surfaces, facies architecture and paleowind direction of the Santai Formation in the east of the Mengyin Basin, western Shandong Province. Three basic types of eolian stratification are recognized in the Santai Formation, including grainflow strata, wind ripple strata and adhesion strata, and have been grouped into eolian dune and interdune facies associations. The occurrences of reactivation surfaces and superimposition surfaces within eolian dune deposits indicate active compound dunes or draas. The association of adhesion strata with grainflow or windripple strata is the development of a wet eolian system. Cross-strata dip direction indicates different paleowind directions from the lower to the upper part of the Santai paleoerg. The lower part of the paleoerg was characterized by paleowinds blowing from northwest to northeast, whereas the upper part was under the influence of paleowinds consistently towards east to northeast. The identified changes in wind directions possibly suggest wind regime shifts from monsoon circulation to westlies of planetary wind system, which may be related with the collapse of the East China Plateau during the Late Jurassic to Early Cretaceous.

Late Jurassic and Early Cretaceous Radiolarians from Zhilong,Gyangse,Tibet

Abundant well-preserved Late Jurassic-Early Cretaceous radiolarian fossils were extracted from 31 bedded green chert samples collected from Zhilong section,Gyangse,southern Tibet.This

Changes of taxonomical composition of Late Jurassic-Early Cretaceous palynofloras of Bureya Basin,Russia

The changes of taxonomical composition of the Late Jurassic- Early Cretaceous palynofloras are revealed, in the upper stream of Bureya River in Bureya Basin. The palynofloras are dominated as follows： the Berriasian one by ferns （Cyatheaceae, Dicksoniaceae, Osmundaceae）, Classopollis and bisaccate pollen; the Valanginiar-Hauterivian one by ferns （Cyatheaceae, Dicksoniaceae）, Ginkgocycadophytus and bisaccate pollen; the Barremian one by ferns （Cyatheaceae, Dicksoniaceae）; the Aptian one by ferns （Cyatheaceae, Dicksoniaceae, Gleicheniaceae） and Ginkgocycadophytus; and the Albian one by ferns （Schizaeaceae） and bisaccate pollen. In the Albian the floral diversity raises with the angiosperms appearing.

Early Cretaceous Tectonism and Diatoms in Korea

The Early Cretaceous Sindong Group, a non-marine molasse, unconformably overlies the folded earliest Cretaceous Myogok Formation. The tectonism that folded the Jaseong Synthem including the Myogok and other formations is here called the Nakdong-Jaeryeonggang （N-J） tectonism. The Oknyeobong and Dabokni Formations are discussed to show that they belong to the Jaseong Synthem. The Dabokni Formation yielded fossil diatoms whose age has been referred as the ＂earliest Cretaceous＂ based on the geologically constrained age of the fossil-bearing deposit. The age of the N-J tectonism appears Barremian as it is between the Hauterivian Myogok Formation and the Aptian Sindong Group with the TPN （Trigonioides-Plicatounio-Nippononaia） fauna. The N-J tectonism, an orogeny, quite deformed pre-Aptian strata in Korea, but can hardly find its reported equivalent in NE China. A revised correlation table shows that the Jaseong- Sindong sequence corresponds to the Jehol Group of China. The Sindong-Hayang transition was characterized by basin migration and dextral rotation probably caused by the Tan-Lu fault system in a broad sense.

Late Jurassic to early Cretaceous magnetostratigraphy of scientific drilling core LK-1 in the Lingshan Island of Riqingwei Basin,eastern China

The Sulu orogenic belt is an uplift zone that was formed in the Late Triassic.Several Jurassic to Cretaceous sedimentary successions have been recognized within the Sulu orogenic belt in recent studies,including outcrops that are considered to be related to the newly discovered Riqingwei Basin.This basin has been the focus of extensive study due to its continuous Cretaceous rock sequence,geological location and petroleum resource potential.However,the lack of a consolidated chronology for the strata has precluded a better understanding of stratigraphy,tectonic evolution and resource potential of the Riqingwei Basin.Here,we present the results of a new magnetostratigraphic study of the continental scientific drilling borehole LK-1,which is located on Lingshan Island,offshore Shandong province,eastern China.The goals of this study are to(1)refine the Late Jurassic to Early Cretaceous chronostratigraphic framework of the Riqingwei Basin,and(2)investigate the location of the J/K boundary in the Borehole Core LK-1.The observed patterns of the paleomagnetic polarity zone in the LK-1 borehole correlate well with the geomagnetic polarity time scale(GPTS),and the continuous magnetostratigraphy profile defined in this core indicates an age ranging from 146.5 to 125.8 Ma for the samples interval.The sediment accumulation rates(SAR)of LK-1 show one period of high SAR(~10.5 cm kyr^(-1))at 135.3–130.6 Ma and two periods of low SAR(~4.8 and~2.2 cm kyr^(-1))at145.7–135.3 and 130.6–125.8 Ma,respectively.In addition,the magnetostratigraphic results suggest that the Jurassic-Cretaceous(J/K)boundary of the LK-1 is located within the magnetozone N21.2 n(~1254 m).This comprehensive geochronologic framework provides a good correlation of the marine Upper Jurassic to Lower Cretaceous strata in the Riqingwei Basin to other marine strata and continental sequences,in addition to providing a foundation for the study of the structural evolution of eastern China.

滇东南薄竹山矿集区晚白垩世岩浆活动及锡银铅锌钨多金属成矿作用

薄竹山锡银铅锌钨多金属矿集区位于华南褶皱系西缘,属于滇东南岩浆成矿带的重要组成部分。区内矿产资源丰富,以锡银锌钨矿床为主,兼有铅锌铁铜等多种金属矿产,矿床均围绕薄竹山岩体分布,其中以白牛厂超大型银多金属矿和官房大型钨矿最为典型。研究表明,薄竹山矿集区锡银铅锌钨多金属矿床的形成与晚白垩世岩浆活动存在密切的联系,其复式岩体成岩时代可以追溯至91.2~84.1 Ma,属晚白垩世岩浆活动的产物。晚白垩世酸性岩浆沿着薄竹山背斜核部与北西向断裂交合地带大规模侵位,在岩浆的顶托作用和底劈作用下,最终形成了薄竹山复式花岗岩体及白牛厂隐伏花岗岩体。薄竹山各单元岩体与白牛厂二长花岗岩、花岗斑体,以及团山、官房花岗岩均表现出一致的富硅(w(SiO_(2))为65.48%~74.92%)、富钾(w(K_(2)O)为4.17%~6.06%)的特征,岩石富集轻稀土元素(LREEs),具中等负铕异常,各岩体明显富集大离子亲石元素(LILEs),而相对亏损高场强元素(HFSEs),为一套准铝质—过铝质的钙碱性—高钾钙碱性S型花岗岩,形成于同碰撞造山及向碰撞后造山环境过渡的大地构造背景,属于造山运动的产物。区内成矿物质迁移与富集主要围绕着花岗岩体进行,发育形成了花岗岩接触带的夕卡岩型W、Sn、Fe矿床,碎屑岩–碳酸盐岩建造中的岩浆热液型Ag、Pb–Zn、Sn、Cu及外围地层中低温热液型Sb矿,这在区域上构成较为完整的与花岗岩侵位有关的岩浆热液成矿系统。

湘东北燕山期动力学背景约束:金井地区花岗质侵入岩年代学和地球化学特征

湘东北地区燕山期岩浆活动频繁,侵入岩广泛发育,但其活动期次和构造背景尚存争议。本文对湘东北金井地区花岗质侵入岩开展了年代学和岩石地球化学研究,厘定了岩浆活动期次、探讨了岩浆活动的构造背景和动力学机制。结果显示侵入岩体锆石SHRIMP U-Pb年龄为165~160 Ma和155~150 Ma,表明岩浆活动(晚侏罗世)可划分为两个期次。侵入岩具有富硅、富铝、富钾、高ASI的特点,总体属高钾钙碱性系列强过铝质花岗岩类,微量元素中Ba、Nb、Sr、P、Ti明显或强烈亏损,Nb相对Ta明显亏损,轻稀土富集且Eu具弱-中等亏损,I_(Sr)值为0.71383~0.72919,ε_(Nd)(t)值为–10.98~–8.47,t_(DM2)为1.64~1.83 Ga,显示源岩主要为中上地壳变质泥质岩和变质杂砂岩,少量为下地壳基性岩,总体属S型花岗岩。结合岩石地球化学特征和区域构造背景,本文提出165~160 Ma的岩浆活动主要与增厚的中上地壳发生减压熔融有关,155~150 Ma的岩浆活动与减压熔融及古太平洋俯冲板块崩塌导致软流圈上涌有关。

Changes of Late Mesozoic Tectonic Regimes around the Ordos Basin(North China)and their Geodynamic Implications

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was established from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozoic tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates （the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west） towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.

Late Mesozoic Chresmodids with Forewing from Inner Mongolia, China (Polyneoptera: Archaeorthoptera)

Three new species of Chresmodidae are described. They belong to two different genera： Chresmoda multinervis sp. nov., Chresmoda shihi sp. nov. and Jurachresmoda sanyica sp. nov.. A study of the forewing venation is provided. Longitudinal veins are mostly parallel; costal area is broad at the basal and narrowing distally; ScP is probably extending close to the wing apex; R is parallel at length to ScP; MA is running close to R, with two long parallel branches; MA branched-off basally; while MP is not branched until the middle of the wing. However, the important basal part of MP and CuP is poorly preserved. In addition, unique fringing hairs on the mid legs of C. shihi sp. nov. and J. sanyica sp. nov. are described and compared with Jurachresmoda gaskelli Zhang, Ren and Shih, 2008.

New Fossil Beetles of the Family Elateridae from the Jehol Biota of China(Coleoptera:Polyphaga)

Two new species of elaterids assigned to two new genera with intriguing fossa on prosternum are described and illustrated： Bilineariselaterfoveatus gen. et sp. nov. and Curtelater wui gen. et sp. nov. from the Upper Jurassic-Lower Cretaceous Yixian Formation of western Liaoning, China. The origin of the clicking mechanism in these beetles and the systematic position of the two genera are briefly discussed.

The Late Mesozoic Orogenic Processes of Mongolia-Okhotsk Orogen: Evidence from Field Investigations into Deformation of the Mohe Area, NE China

Based on field investigation in 1999, two deformational domains with d ifferent dynamics have been distinguished from the Jurassic geological outcrops in the Mohe area of NE China, i.e. northern ductile and southern plastic-brittl e ones. Their deformational features are stated in this paper. And then, three st ages of structural deformation of the area relative to the late Mesozoic orogeni c processes of Mongolian-Okhotsk orogen are reconstructed as follows, (1) south w ards thrusting in the middle-late Jurassic, (2) eastwards thrusting and strike -s lipping parallel to the orogen in the late Jurassic, and (3) southeastwards thru sting in the early Cretaceous.

商丹俯冲增生带南缘土地沟–池沟地区侵入岩形成时代及地质意义

位于商丹俯冲增生带南缘山阳–柞水地区的侵入岩类在形成时代主要集中在新元古代(885~621 Ma)和中晚三叠—早白垩世(233~132 Ma)2个阶段,且后者多为秦岭造山带印支期—燕山期造山活动的产物。该构造带内土地沟至池沟地区出露有部分与成矿作用有关的小岩体,锆石LA–ICP MS U–Pb同位素测年结果表明其形成时代为144.4~158.8 Ma,属于晚侏罗世—早白垩世侵入岩类。岩石地球化学特征显示出富集大离子亲石元素,亏损高场强元素,高Sr、低Y的特征。结合区域岩浆岩演化研究,可以认为土地沟–池沟地区晚侏罗—早白垩世侵入岩类的形成可能与西太平洋活动应力作用以及区内的北西向构造系统约束具有密切关联。受此影响,以中南秦岭地区在后碰撞–后造山阶段拆沉和幔源物质上涌作用下,地壳物质发生重熔从而在山阳–柞水一带形成一系列中酸性侵入岩类。

内蒙古中东部玛尼吐组火山岩形成时代及其大地构造环境

玛尼吐组广泛分布在内蒙古中东部地区,长期以来与满克头鄂博组和白音高老组的地质时代被定为晚侏罗世,然而前人在玛尼吐组中发现Nestoriapissovi化石,并认为是早白垩世冀北阶的带化石,同位素年代学结果差异也较大,而且形成的大地构造环境仍然存在争论。因此,笔者对玛尼吐组火山岩进行了同位素年代学分析,并利用全岩成分探讨其形成的大地构造环境。玛尼吐组采集的3个安山岩和粗安岩的锆石U–Pb(LA–ICP–MS)测年结果分别为(142.4±1.4)Ma、(130.0±1.4)Ma和(145.0±1.5)Ma,显示该地区玛尼吐组形成于早白垩世。样品SiO2含量为59.43%~64.73%,Al_(2)O_(3)含量为15.66%~17.19%,K_(2)O含量为2.56%~5.03%,Na_(2)O含量为3.59%~4.53%,全碱含量为6.36%~9.56%;微量元素以富集大离子亲石元素和LREE,亏损Nb、Sr、P和Ti为特征;稀土元素ΣREE=118.71×10^(–6)~189.99×10^(–6),轻重稀土分馏系数(La/Yb)N为8.88~9.58,δEu值为0.66~0.95,Eu负异常,与岛弧火山岩地球化学特征相似。对比大兴安岭西部玛尼吐组西部、中部(~140 Ma)和东部火山岩年龄,笔者认为其玛尼图组火山岩类最老形成于晚侏罗世(~158 Ma),向东逐渐变新为早白垩世(140~130 Ma),这一变化与蒙古–鄂霍次克洋自西向东的闭合及陆块的后碰撞伸展有关。

西昆仑-塔西南坳陷晚古生代以来的沉积构造演化

自柯克亚深层油气勘探取得突破以来,塔西南坳陷一直受到各类地质学家的广泛关注,有关该盆地的形成和演化历史及其油气资源评价近年来更是成为人们的研究热点。本文在总结前人资料的基础上,探讨塔西南和西昆仑地区自晚古生代以来所经历的构造及沉积格架的演变过程,对塔西南坳陷性质及其演化阶段划分所存在的争议进行了归纳,分析了塔西南-西昆仑这一盆山体系形成和演化中的构造变形和沉积记录。总体来说,根据现有沉积和构造变形资料,中生代之前西昆仑和塔西南坳陷分别处于同一构造背景下的不同沉积单元;二者之间盆山体系的形成主要自晚侏罗世-早白垩世,中-上新世是造盆造山作用机制发生重大转折的时期,或者说早更新世末的构造运动基本上奠定了西昆仑-塔里木盆地南缘现今的盆-山构造格架。

冈底斯中北部晚侏罗世—早白垩世地球动力学环境:火山岩约束

利用新近完成的1∶25万区域地质调查资料和笔者分析数据,初步研究了西藏冈底斯带晚侏罗世—早白垩世火山岩的分布特点及地层古生物、同位素年代学约束的火山活动时代以及冈底斯中北部火山岩的性质、构造环境、岩石成因和俯冲极性。冈底斯带晚侏罗世—早白垩世火山岩主要分布于南冈底斯、中冈底斯、北冈底斯和班公湖-怒江缝合带南缘,基本同期开始于早白垩世(大约120～130 Ma)并可能延续到晚白垩世,以冈底斯中北部地区规模最大为特征。已有数据显示中冈底斯则弄群火山岩包括部分中钾钙碱性系列的中基性岩石和占优势的高钾钙碱性系列的中酸性火山岩,不同于传统岛弧火山岩,但与中安第斯厚地壳背景下的岛弧火山岩相似,北冈底斯主要为与传统岛弧火山岩相似的中钾钙碱性系列火山岩。中冈底斯则弄群中基性火山岩很可能与来自消减沉积物和/或蚀变玄武质洋壳的含水流体引起上覆地幔楔物质的部分熔融有关,并在岩浆上升过程中经历了明显的分离结晶作用和中上部地壳物质的同化混染(即AFC过程),长英质火山岩很可能主要与地壳重熔有关,但并不能完全排除镁铁质岩浆的分离结晶作用。目前冈底斯中北部晚侏罗世—早白垩世火山岩地球化学数据揭示的成分变化、地壳厚度、与俯冲带的距离以及冈底斯带同期火山岩的分布特点暗示冈底斯中北部火山岩很可能与班公湖-怒江特提斯洋壳向南的俯冲作用有关。

新特提斯演化的热点与洋脊相互作用：西藏南部晚侏罗世-早白垩世岩浆作用推论

雅鲁藏布蛇绿混杂岩代表了新特提斯洋盆闭合的地表残余。本文在测试数据基础上,综合分析了目前雅鲁藏布江蛇绿混杂岩研究中取得的比较可信的晚侏罗世-早白垩世玄武岩的地球化学数据,并对其进行了较为详细的区域对比分析以讨论涉及新特提斯演化的地球动力学过程。结果表明:(1)雅鲁藏布蛇绿混杂岩带吉定洞拉村玄武岩、错拉山口北部玄武岩为大洋中脊玄武岩(MORB)型,错拉山口南部玄武岩为洋岛玄武岩(OIB)型,萨嘎桑单林玄武岩既包括OIB型,又包括MORB型;(2)在东西延伸约1500km的雅鲁藏布蛇绿混杂岩带中,至少可能存在OIB、MORB(包括N-MORB、E-MORB)和岛弧玄武岩IAB三种类型的晚侏罗世-早白垩世玄武岩。不活动的高场强元素比值(如Nb/Y,Zr/Y等)指示雅鲁藏布蛇绿混杂岩带中部仁布、杯玛让、吉定洞拉村和错拉山口北部地区以及中西部萨嘎地区的MORB型玄武岩中的亏损组分很可能来源于深部亏损的地幔柱源区。微量元素地球化学模拟表明,雅鲁藏布蛇绿混杂岩带OIB型玄武岩可能主要来源于石榴石二辉橄榄岩源区中等程度(10%～20%)的部分熔融,而MORB型玄武岩主要来源于尖晶石二辉橄榄岩源区中等程度(7%～25%)的部分熔融,IAB型玄武岩所代表的源区熔融深度以中部较浅而东西两端较深为特点,其中中部得几、杯玛让、吉定等地的IAB很可能与尖晶石二辉橄榄岩源区的部分熔融有关,而东部和西部达几翁IAB的熔融源区可能残留有石榴石。结合该带报道的He同位素数据和矿物学观察,以及在喜马拉雅带新获得的古地磁数据,可以认为热点与洋脊的相互作用是对晚侏罗世-早白垩世新特提斯演化的一种很可能的地球动力学解释。需要强调,虽然该模式可以较好地解释目前在藏南观察到的晚侏罗世-早白垩世岩浆作用特点和性质,但因资料有限,还需要做许多非常细致的工作来证实或否定。

南岭地区大规模钨锡多金属成矿作用：成矿时限及地球动力学背景

南岭位于华南地区中部,是我国乃至全球最主要的钨锡金属成矿省。本文基于最近几年的高精度成岩成矿测年资料和地球动力学研究进展,提出南岭地区大规模成矿作用出现于中晚侏罗世(165～150Ma),相应的构造背景是古太平洋板块向大陆俯冲,在大陆边缘弧后地区出现一系列NE向壳幔相互作用强烈的伸展带,这些伸展带与东西向古断裂的交汇部位是岩浆活动和成矿作用中心区,NE向十杭带与南岭中脊部EW向古深大断裂的交汇处形成湘南最大的钨锡矿集区。在中晚白垩世,古太平洋板块向NNE方向走滑,导致大陆岩石圈大面积伸展,相应大规模的火山活动主要出现在武夷山以东地区,但在包括南岭地区在内的华南地区广泛出现盆岭构造,NNE向的白垩纪红层-火山盆地与以花岗岩为代表的隆起相间分布,在一些盆地可见130～90Ma侵位的、面积不大却广泛分布的花岗岩及其锡多金属矿化,构成华南地区大规模锡多金属矿化作用,但这次成矿作用在南岭地区并不十分强烈。

华北晚侏罗世—早白垩世风成砂沉积及其古地理和古生态学意义

华北晚侏罗世—早白垩世风成砂主要分布于鲁西蒙阴盆地上侏罗统三台组、辽西金—羊盆地上侏罗统—下白垩统土城子组、冀西北尚义盆地上侏罗统—下白垩统土城子组/后城组(原阎家窑组)、鄂尔多斯盆地下白垩统志丹群和甘肃下白垩统河口群。各地风成砂岩均具高角度大型—巨型板状、楔状交错层理及平行层理,分选较好—好,磨圆次棱角状—次圆状等沉积特征。对华北晚侏罗世—早白垩世风成砂赋存层位以及风成砂岩形成时代进行了对比,将风成砂主要划分为3个时期,即基末利期—贝利阿斯期、凡兰吟期—欧特里夫期和欧特里夫期—阿普特期,且从鲁西到甘肃风成砂岩形成时代逐渐变新。通过上述5个地区风成砂的古风向研究发现,当时西北风盛行,古地磁研究显示风成砂岩发育于N25°—N45°之间区域。根据当前全球风带分布特征,认为华北晚侏罗世—早白垩世处于西风带上,为行星风系所控制。通过对比南半球同期风成砂岩古风向研究,提出全球南北半球中纬度地区均处于西风带上。结合风成砂及相应层位沉积特征、沉积环境的研究,初步推测晚侏罗世—早白垩世,华北N30°以北地区为干旱寒冷气候,而N30°以南地区则干旱炎热,华北北部整体处于海拔较高的山地环境,山间盆地发育,火山活动频发。燕辽生物群与热河生物群的演替过程与风成砂沉积相耦合,体现了古地理、古环境对生物群发展的制约作用。

藏南羊卓雍错南部桑秀组火山岩的特征及构造环境

羊卓雍错南部桑秀组中分布有由玄武岩-安山岩-英安岩构成的海相火山岩组合,区域露头上玄武岩占绝对优势,喷发时代为晚侏罗世晚期—早白垩世早期。区域资料显示,这一时期该地区处于冈瓦纳大陆的被动陆缘。地球化学特征表明,本区火山岩与洋脊玄武岩和洋岛型玄武岩有明显区别,显示大陆拉张带或大陆裂谷亚碱性拉斑玄武岩的特征。

大兴安岭中北部晚侏罗世—早白垩世地层新认识

根据大兴安岭中北部地区晚侏罗世火山岩正常沉积夹层中所含叶肢介化石的研究成果和同位素年龄新资料,认为大兴安岭北部西坡被归入白音高老组中的“含Eosestheria的酸性、酸碱性火山碎屑岩和熔岩”不是白音高老组,应归入龙江组,层位与辽西义县组对比。大兴安岭主脊火山岩(满克头鄂博组、玛尼吐组、白音高老组)从南到北是同期火山活动作用的结果,不存在“穿时”现象,形成于晚侏罗世早中期,层位与冀北大北沟组对比。